DC--DC converters are normally used as constant DC voltage power supplies. The desirability of having a DC--DC converter that provides a number of different voltage outputs to a number of different independent loads has been recognized. There is a continuing need for such a circuit which is of relatively simple construction and relatively inexpensive, and which provide stable voltage levels to a number of independent loads that, if desired, can be electrically isolated. With electrical isolation, noise, impedance changes, and the like from one load would not affect the power transmitted to another load.
Multiple output DC--DC converters providing a regulated voltage have typically required separate outputs provided by separate transformer windings as well as independent direct voltage regulating controls for each output where precise regulation is required. In a typical forward or flyback converter with multiple outputs, the non-conduction intervals of the power switch may result in a noncontinuous transfer of energy to the output which results in an inefficient transfer of energy to the output.
Magnetic amplifiers have been used as pulse width modulators in DC--DC converters because of their high reliability and current surge suppression characteristics. In addition, the size of the magnetic amplifier can be made small in the high frequency switching. When multiple non-interactive outputs are required from a single DC--DC converter, magnetic amplifiers are suitable as pulse width modulator elements, since it is easy to control the duty ratio in the secondary circuit of the transformer and to isolate the input and output. However, the use of magnetic amplifiers as pulse width modulators may cause a limit on the maximum duty cycle which limits the available power. Magnetic amplifiers also, in some application, are too large in size, and are expensive components of a DC--DC converter.
A need has thus arisen for a self-synchronized pulse width modulator to provide regulation in a multiple output converter which is small in size, inexpensive, and provides improved performance over magnetic amplifiers.